This invention pertains generally to magnets and more particularly pertains to magnetic decouplers for use with antitheft devices.
A known antitheft device for use in stores selling such goods as clothing or dry goods comprises a disc that sets off an alarm if taken out of the store. One typical disc of this type is manufactured by the Knogo Corp., of Hicksville, New York, and sold under the trade name THE KNOGO WAFER. The disc is attached to the goods to be protected by means of a tapered pin inserted through the goods and into one side of the disc. The length of the pin is greater than the thickness of the disc, and the side of the disc opposite that into which the pin is inserted is provided at its center with a nipple in which the pin is accommodated, so that the full length of the pin can be inserted into the disc. The pin has at least one circumferential groove. The nipple contains a mechanism for engaging the groove in the pin, which mechanism is constructed so that the pin can be easily inserted into it but, once inserted, cannot be withdrawn until the gripping mechanism can be made to disengage the groove. As a result, a potential thief cannot remove the disc from an article of merchandise. A special magnetic decoupler used to permit the removal of the disc by the clerk when the article is purchased. The magnetic decoupler includes a cavity into which the nipple is inserted, and a permanent magnet of suitable design provides a magnetic field in the cavity with a flux in such a direction within the cavity as to force the gripping mechanism in the nipple to disengage from the groove, allowing removal of the pin from the disc.